1. Field of the Invention
The present invention relates to a deterioration diagnostic method and equipment thereof that will diagnose the progressive corrosion deterioration during use, the deterioration of electrical properties and, consequently, the life span, of the metallic materials, of the metallic material parts that compose electronic circuits and of the electronic circuit boards that compose electronic apparatus.
2. Description of the Related Art
First, prior art relating to diagnosis of corrosion deterioration of general metallic materials in atmosphere will be described. The effects of atmospheric temperature and relative humidity and the various types of corrosive gas and the sea salt particles present in the atmospheric environment cause chemical reactions and promote corrosion in metallic materials used in an atmospheric environment. The atmospheric environments in which metallic materials are used are multifarious. There are various kinds of environment such as environments in which temperature and humidity are controlled and hardly any corrosive gases or sea-salt particles are present, like clean rooms, environments with high hydrogen sulfide gas concentrations, like geothermal power stations, and environments close to the seashore where sea-salt particles are always in the air. Moreover, corrosion-resistive performances in atmospheric environments also vary depending on the type of metallic material.
In the past, the method adopted for the diagnosis of corrosion deterioration of metallic materials used in atmospheric environments was to expose the metallic material that was the subject of diagnosis for a specified period in the environment in which it was to be used, retrieve the material and measure the corrosion loss, find the corrosion speed from the exposure period and the corrosion loss, and estimate the life expectancy (life span or duration of life). However, since, with the corrosion of metals, there is a tendency for the corrosion speed to reduce with the passage of time, differences will arise in the corrosion speed depending on the period of exposure of the metal. There are also differences according to the season (summer or winter) in which exposure is commenced. Thus, to estimate the corrosion progress of a metal with good accuracy, long-term exposure tests using a number of exposure periods were mandatory. Also, there was the problem that, each time the value of even one factor of the environment changed there would be a requirement to carry out exposure tests of the metal.
Moreover, a method has also been adopted of diagnosing the corrosion life of a metallic material by carrying out corrosion tests of the metallic material using accelerated test equipment that simulates acceleration of the atmospheric environment, and multiplying the life span by the acceleration factor of the accelerated test. However, it is difficult to simulate an actual atmospheric environment as an accelerated test, and the accuracy of the acceleration factor was poor because of differences between environmental factors and set conditions, and thus accurate diagnosis of the life of a metallic material was very difficult.
Furthermore, a system of classifying an environment and assigning evaluation points to each environmental factor according to the range of its measured values, totalling the assessment points of the various environmental factors, and judging the environment by the total assessment points has been adopted by Computer Installation Environmental Standard for Industry JEIDA-29-1990 of the Japanese Electronic Industry Development Association. However, this is strictly only used for dividing environments into classes and cannot be applied to assessing the deterioration state of a metal or diagnosing its life.
As described above, with prior art, to perform diagnosis of the corrosion state and the deterioration state of a metallic material that was used in an atmospheric environment, or the diagnosis of its corrosion life, long-term metallic material exposure tests had to be carried out in each case. This took a vast amount of time and expense and, moreover, high-accuracy life diagnosis was not possible.
Next, prior art relating to the diagnosis of the deterioration of electrical properties through corrosion of the metallic material parts that compose electronic circuits used in atmospheric environments will be described. With an electronic circuit board used in an atmospheric environment, the metallic materials that compose the electronic circuit, such as for instance the copper of the wiring material, the steel of integrated circuit lead terminals, soldered parts and the metal-plating of contact terminals, corrode due to the effects of environmental factors in the atmosphere, such as for instance temperature, humidity, various types of corrosive gases and sea-salt particles. If the influence exerted on the metallic materials by the environmental factors is great, the corrosion of the relevant parts of an electronic circuit board will be severe, electrical malfunctions will occur, such as wiring breaks, insulation drops or short-circuits due to migration, and contact damage, and the board's life will end. The following two items of prior art relate to assessment of the deterioration due to migration out of the above. First, Japanese Laid-Open Patent Publication No. Heisei 6(1994)-11530 Gazette, “Assessment Method and Equipment for the Insulation Reliability Life of Electronic Parts”, concerns a method of assessing the lives of printed wiring boards, electronic parts and the like from their insulation reliability and, in particular, proposes a good life assessment method for performing early diagnosis of life due to migration deterioration. It is a method of measuring insulation resistance or leak currents as initial and last-off dielectric characteristics, and judging the life from the time-wise variation of those characteristics.
Next, Japanese Laid-Open Patent No. Heisei 7(1995)-249840 Gazette, “A Printed Board and Method of Diagnosing Its Deterioration”, proposes a method for the quantitative diagnosis of deterioration such as corrosion in printed boards and short-circuits caused by migration. It is a deterioration diagnosis method of pre-printing a pair of electrode conductors for deterioration diagnosis on a printed is board, measuring the dielectric tangent factor in the low-frequency domain between the two electrode conductors, and estimating the time to occurrence of a short-circuit between the two electrode conductors based on the value of that dielectric dissipation factor.
Since the conductor widths of conductors on electronic circuit boards in the past were broad, there were often cases when there was corrosion of the conductors due to the effect of atmospheric environmental factors but insulation deterioration due to migration and the like occurred first, and then corrosion of the conductors progressed and led to breaks in conductors. The prior art insulation deterioration diagnostic method described above was effective with the deterioration of this type of electronic circuit board. However, in recent years, narrowing of electronic circuit board conductors has progressed and there are many cases in which conductors break before insulation deterioration due to migration occurs. Thus, the above deterioration and life diagnostic method is no longer appropriate for forecasting conductor breakages. Therefore, in the case of forecasting conductor breakage life, a method was produced in which a conductor part of the relevant electronic circuit board was cut and, by observing the cross-section of the conductor, the remaining life was estimated from the remaining conductor thickness. For that purpose, a working item was taken as the product and, because it was a destructive test, a new electronic circuit board had to be adjusted and supplied in place of the board taken.
As used herein, the term “migration” means the phenomenon of migration of metallic atoms produced by electrolysis.
This is the phenomenon that, when an electric field is applied between metals under conditions of high humidity, the metal of the electrode on the high-potential side is ionized (phenomenon similar to electrolysis in water), and migrates towards the metal of the electrode on the low-potential side, ultimately creating a short circuit between the electrodes. Migration occurs more rapidly with increased humidity, increased DC electrical field, and increased contamination of the circuit board surface. That is, migration becomes more likely to occur as leakage current between the metal electrodes is facilitated. The migration that is here referred to is migration of solder in the area where the component leads are mounted on an electronic circuit board and/or migration of copper of the adjacent wiring pattern.
Moreover, for life assessment of electronic circuit parts other than electronic circuit boards, a method was used of assessing the lives of the electronic parts on a printed circuit board that composed a equipment by removing the individual parts from the board, carrying out accelerated deterioration tests, and measuring their specialized electrical characteristics. In the case of the former, failure judgements are performed by applying deterioration stress and confirming the performances of the parts. Then, the progression of cumulative failure rates for accelerated test times are deduced for each of the various types of parts, and the life point is defined at the desired cumulative failure rate An example of this is Japanese Laid-Open Patent No. Heisei 10(1998)-313034 Gazette. With this, in the case of assessing the life of a resin-sealed type IC, the IC resin package that has been removed from the board is unsealed and the corrosion state of the aluminium wiring on the IC chip inside is observed. Thus, early detection of corrosion and quantitative remaining life assessment of ICs that display defective logic or malfunctions is achieved by image measurement of the corrosion area percentage of the aluminium wiring. Also, as an example of the latter, in the case of the silver contacts that compose an electronic circuit, corrosion films are formed on the silver contact surfaces through the effects of atmospheric environmental factors and contact resistance increases and defective contact occurs. Therefore an electronic part, having silver contacts, that has been used in the relevant environment is removed, and the deterioration state of that part is judged by measuring the contact resistance of that part.
Next, the diagnosis of progressive electrical characteristic deterioration during use due to soiling of electronic circuit board surfaces will be described for electronic circuit boards that compose electronic apparatus. When electronic circuit boards are used in an atmospheric environment, dust floating in the atmosphere adheres to their surfaces and accumulates with time. Since various corrosive gases and sea salt particles present in the atmospheric environment adsorb such dust, if the humidity becomes high, ionic substances (e.g. such as chlorine ions, sulfuric acid ions, nitric acid ions and sodium ions) will ionically dissociate to become the cause of reduced insulation of the electronic circuit board surface and corrosion of the conductor pattern metals. In particular, since dust will accumulate locally on electronic circuit boards in control panels that are forcibly cooled by using fans, there will be many instances of insulation reduction and conductor pattern breakage phenomena in the short term. In such cases also, the technique of destroying part of the circuit on the board is often adopted for studying the insulation resistance values and conductor pattern corrosion states on soiled electronic circuit boards.
In the above way, in order to diagnose the various types of deterioration concerned in the corrosion of, and the lives of, metallic material parts that compose electronic circuit boards and to study the insulation resistance values and conductor pattern corrosion states of soiled electronic circuits, part or all of the relevant circuits or parts must be removed. In other words, it is essential to carry out destructive testing of the circuits or parts. This not only requires a great deal of labor and expenditure but, with this method there is the great problem that, even if, as a result of diagnosis, it is confirmed that the remaining life of the equipment is satisfactory, that equipment cannot be re-used after diagnosis, and it will be necessary freshly to adjust an electronic circuit and assemble it into the electronic apparatus.
Also, there were methods of measuring heat distribution as methods of deterioration diagnosis of electronic circuit boards. However, to measure heat distribution, it was necessary to remove the electronic circuit board, and measure the heat distribution of the board as a whole by freshly inputting a power source. As an example of this, there is Japanese Laid-Open Patent No. Heisei 11(1999)-14576 Gazette, “Deterioration Diagnosis and Equipment for Mounting Boards”. With this, the temperature distribution until the surface temperature of the mounting board achieves the steady state after power source input is measured, and the temperature-rise image data that have been converted to images are compared with past temperature-rise image data. The amount of variation of temperature distribution between the two is calculated, and when this value exceeds a pre-set threshold there is judged to be deterioration. With this method, there is no need to destroy the electronic circuit board but specialised analysis equipment for thermal distribution images is required.
With prior art there were such problems as the following. Exposure testing of metallic materials over a long period was indispensable for the diagnosis of the corrosion, deterioration state and corrosion life of metallic materials used in atmospheric environments. Also, for the diagnosis of the corrosion states of the various types of electrical characteristics concerned in the corrosion of metallic material parts that compose electronic circuits, and for the diagnosis of the corrosion states and insulation deterioration states of electronic circuit boards that compose electronic apparatus, those electrical characteristics could only be tested by partial or complete withdrawal and destructive testing of those metallic material parts and electronic circuit boards. Moreover, those parts and boards could not be re-used after diagnosis. Furthermore, although diagnosis by thermal distribution imaging was non-destructive, specialized diagnostic equipment was required, and it was not suitable for general use.